1. Technical Field
The invention relates to a testing apparatus and a method for conducting tests of compatibility on wellbore fluids and their contaminated mixtures and slurries under specific pressure and temperature conditions and, in particular, an apparatus and method for testing fluid mixtures and slurries for use in subterranean wellbores under simulated wellbore conditions.
2. Background Art
When drilling, completing, and treating subterranean hydrocarbon wells, it is common to inject materials fluid form with complex structures, such as, suspensions, dispersions, emulsions and slurries. These injected materials are present in the wellbore with materials such as water, hydrocarbons, and other materials originating in the subterranean formations. The materials present in the wellbore will be referred to herein as “wellbore fluids” or “wellbore liquids.” These substances and their mixtures flow rather than plastically deform. The flow of these fluids and mixtures cannot be characterized by a single value, instead the apparent viscosity and shear stress changes due to other factors such as temperature and pressure and the presence of other materials. Indeed, the materials in some mixtures may be characterized as incompatible. Two fluids are incompatible if undesirable physical and/or chemical interactions occur when the fluids are mixed. Many times incompatibility is characterized by apparent viscosity and shear stress. When apparent viscosity of fluids A and B combined is greater or lesser than apparent viscosity of fluid A as well as apparent viscosity of fluid B, then fluid A and fluid B are said to be incompatible at the tested shear rate.
Cement is placed in wellbore annulus to block or seal off fluid flow, isolate hydrocarbon zones, and provide support for well casings. Wellbores typically are at elevated temperatures and pressures, and contain contaminating fluids and solids. The flow characteristics of various cement mixtures are estimated based on the testing of cement in the presence of a contaminant, such as a fluid spacer, drilling mud, salt water brines or hydrocarbons. In addition, mixtures of spacer fluids and drilling mud are also tested. Other examples, including mixtures of wellbore fluids pumped into the wellbore to carry particulate in suspension to the hydrocarbon bearing formations, are located outside the wellbore.
It is common to determine optimum wellbore liquids and incompatibility of those liquids in a laboratory by running a series of tests of different liquid mixtures under wellbore conditions. Testing various ratios of mixtures of wellbore liquids is done to replicate the changes in the wellbore concentrations of the fluids, either due to contamination with what is pumped downhole or what may exist downhole. These wellbore liquids and mixtures that have variable viscosity are sometimes called “non-Newtonian fluids.” Testing a series of samples of actual wellbore mixtures during well treatment is also common. Viscosity, elasticity, shear stress, and consistency are rheological characteristics that need to be measured for a given fluid or mixture.
Known devices used to test fluids for these characteristics include viscometers, rheometers, and consistometers. Testing comprises filling a test chamber with a fluid mixture, bringing the chamber to pressure and temperature test conditions, and then conducting tests of the fluids characteristics. In prior art devices the successive test of different mixture ratios requires emptying and refilling the test chamber with a different mixture to repeat the test. As this process requires pressurization/depressurization and heating/cooling to be done every time the sample is changed, this process consumes a lot of time in preparation of the test for well bore conditions.